12,932 research outputs found

    Coulomb correlation in presence of spin-orbit coupling: application to plutonium

    Full text link
    Attempts to go beyond the local density approximation (LDA) of Density Functional Theory (DFT) have been increasingly based on the incorporation of more realistic Coulomb interactions. In their earliest implementations, methods like LDA+UU, LDA + DMFT (Dynamical Mean Field Theory), and LDA+Gutzwiller used a simple model interaction UU. In this article we generalize the solution of the full Coulomb matrix involving F(0)F^{(0)} to F(6)F^{(6)} parameters, which is usually presented in terms of an m\ell m_\ell basis, into a jmjjm_{j} basis of the total angular momentum, where we also include spin-orbit coupling; this type of theory is needed for a reliable description of ff-state elements like plutonium, which we use as an example of our theory. Close attention will be paid to spin-flip terms, which are important in multiplet theory but that have been usually neglected in these kinds of studies. We find that, in a density-density approximation, the jmjjm_j basis results provide a very good approximation to the full Coulomb matrix result, in contrast to the much less accurate results for the more conventional m\ell m_\ell basis

    ENV-654: NUMERICAL MODELLING OF SMOULDERING COMBUSTION TO OPTIMIZE EX SITU SOIL TREATMENT SYSTEM DESIGN

    Get PDF
    There is widespread soil contamination at thousands of cites in Canada resulting from the historical improper storage and disposal of industrial liquids (Story et al., 2014). Large financial resources are allocated to remediation efforts due to the human and environmental health risks associated with exposure to such contamination, with over $582 million CAN spent on remediation in 2014-15 by the Canadian government alone (Treasury Board of Canada, 2016). Our scientific understanding of site remediation has evolved greatly over the past decades and it is now widely accepted that remediation of the contaminant source zone is necessary to achieve a high level of long-term remediation (Kueper et al., 2014). Non-aqueous phase liquids, or NAPLS, are one of the most prevalent contaminants at contaminated sites and are challenging to remediate due to their highly recalcitrant nature (Kueper et al., 2003). Although many remediation technologies have been developed over the past decades, the challenge in source zone remediation of NAPLs persists. The application of smouldering combustion to treat NAPL contaminated soils has been proven as an effective technology with both the laboratory experiments and applied in situ at a field site (Switzer et al., 2009, Pironi et al., 2011, Switzer et al, 2014, Salman et al., 2015, Scholes et al., 2015). This technology, titled “Self-sustaining treatment for active remediation”, or STAR, utilizes the high calorific value of NAPLs to ignite and sustain a smouldering oxidation reaction, effectively destroying the contaminant in the process. A phenomenological model developed by MacPhee et al. (2012) uniquely combined a multiphase flow model, perimeter expansion model, and analytical expression for the forward smouldering front velocity. This model is able to predict the propagation of the reaction front in response to the interplay between a heterogeneous distribution of permeability and the time-dependent distribution of air flux. After subsequent calibration by Hasan et al. (2014), the model was shown to correctly predict the ultimate extent and time of remediation during treatment for 2D lab scale experiments

    Calculation of the two-photon decay rates of hydrogen-like ions by using B-polynomials

    Full text link
    A new approach is laid out to investigate the two photon atomic transitions. It is based on application of the finite basis solutions constructed from the Bernstein Polynomial (B-Polynomial) sets. We show that such an approach provides a very promising route for the relativistic second- (and even higher-order) calculations since it allows for analytical evaluation of the involved matrices elements. In order to illustrate possible applications of the method and to verify its accuracy, detailed calculations are performed for the 2s_{1/2}-1s_{1/2} transition in neutral hydrogen and hydrogen-like ions, and are compared with the theoretical predictions based on the well-established B-spline-basis-set approach

    QED effects on individual atomic orbital energies

    Get PDF
    Several issues, concerning QED corrections, that are important in precise atomic calculations are presented. The leading QED corrections, self-energy and vacuum polarization, to the orbital energy for selected atoms with 30 ≤ Z ≤ 118 have been calculated. The sum of QED and Breit contributions to the orbital energy is analyzed. It has been found that for ns subshells the Breit and QED contributions are of comparative size, but for np and nd subshells the Breit contribution takes a major part of the QED+Breit sum. It has also, been found that the Breit to leading QED contributions ratio for ns subshells is almost independent of Z. The Z-dependence of QED and Breit+QED contributions per subshell is shown. The fitting coefficients may be used to estimate QED effects on inner molecular orbitals. We present results of our calculations for QED contributions to orbital energy of valence ns-subshell for group 1 and 11 atoms and discuss about the reliability of these numbers by comparing them with experimental first ionization potential data.Fil: Koziol, Karol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; ArgentinaFil: Aucar, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentin
    corecore